<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
	</head>
	
	<body>
	<input id="num" />
	<br />
	<input type="button" onclick="one()" value="1" />
	<input type="button" onclick="two()" value="2" />
	<input type="button" onclick="three()" value="3" />
	<input type="button" onclick="c()" value="c" />
	<script>
		var one=function(){
			num.value=num.value+"1";
		}
		var two=function(){
			num.value=num.value+"2";
		}
		var three=function(){
			num.value=num.value+"3";
		}
		var c=function(){
			num.value="";
		}
	</script>
	</body>
</html>
